I don't expect that the Nova has learning capability, but if it does, you should get a 2 blink response to the 975 command.  

If you're really going to try to enter many of the Yamaha codes, consider buying a USB to TTL interface cable--like one of the ones mentioned in this thread.  Then you can manage everything by computer.  

Thanks for checking the signature.  That tells us that the Nova is a JP1.4 remote, and it will communicate with cables intended for JP1.2/1.3 remotes.